This invention relates to processes for making paper and paperboard from a cellulosic stock, employing a novel flocculation system in which a new micropolymer technology is employed.
During the manufacture of paper and paperboard, a cellulosic thin stock is drained on a moving screen (often referred to as a machine wire) to form a sheet, which is then dried. It is well known to apply water-soluble polymers to the cellulosic suspension in order to effect flocculation of the cellulosic solids and enhance drainage on the moving screen.
In order to increase output of paper, many modern papermaking machines operate at higher speeds. As a consequence of increased machine speeds, a great deal of emphasis has been placed on drainage and retention systems that provide increased drainage and retention of the papermaking components. It is known that increasing the molecular weight of a polymeric retention aid (which is generally added immediately prior to drainage) will tend to increase the rate of drainage, but will also damage formation. It can be difficult to obtain the optimum balance of retention, drainage, drying and formation by adding a single polymeric retention aid, and it is therefore common practice to add two separate materials in sequence or jointly.
More recent attempts to improve drainage and retention during papermaking have used variations on this theme by using different polymers and siliceous components. These systems can consist of multiple components.
U.S. Pat. No. 4,968,435 describes a method of flocculating an aqueous dispersion of suspended solids which comprises adding to, and mixing with the dispersion, from 0.1 to 50,000 parts per million of dispersion, solids of an aqueous solution of a water-insoluble, crosslinked, cationic, polymeric flocculent having an unswollen number average particle size diameter of less than 0.5 micrometers, a solution viscosity of 1.2 to 1.8 centipoise, and a crosslinking agent content above 4 molar parts per million, based on the monomeric units present in the polymer, to flocculate the suspended solids, and separating the flocculated suspended solids from the dispersion.
U.S. Pat. No. 5,152,903 is a continuation of this patent, and describes a method of flocculating a dispersion of suspended solids that comprises adding to, and mixing with the dispersion, from 0.1 to 50,000 parts per million of dispersion solids of an aqueous solution of a water-soluble, crosslinked, cationic, polymeric flocculent having an unswollen number average particle size diameter of less than 0.5 micrometers, a solution viscosity of from 1.2 to 1.8 centipoise and a crosslinking agent content above 4 molar parts per million based on the monomeric units present in the polymer.
U.S. Pat. No. 5,167,766 further describes a method of making paper which comprises adding to an aqueous paper furnish from 0.05 to 20 pounds per ton, based on the dry weight of paper furnish solids, of an ionic, organic, crosslinked polymeric microbead, the microbead having an unswollen particle diameter of less than 750 nanometers and an ionicity of at least 1%, but at least 5%, if anionic and used alone.
U.S. Pat. No. 5,171,808 is a further example which describes a composition comprising crosslinked anionic or amphoteric polymeric micropolymers derived solely from the polymerization of an aqueous solution of at least one monomer, the micropolymers having an unswollen number average particle size diameter of less than 0.75 micrometers, a solution viscosity of at least 1.1 centipoise, a crosslinking agent content of 4 molar parts to 4000 parts per million, based on the monomeric units present in the polymer, and an ionicity of at least 5 mole percent.
U.S. Pat. No. 5,274,055 describes a papermaking process wherein improved drainage and retention are obtained when ionic, organic microbeads, of less than 1,000 nanometers in diameter if crosslinked or less than 60 nanometers in diameter if non crosslinked, are added either alone or in combination with a high molecular weight organic polymer and/or polysaccharide. Further addition of alum enhances drainage formation and retention properties in papermaking stock with and without the presence of other additives used in papermaking processes.
U.S. Pat. No. 5,340,865 describes a flocculant comprising a water-in-oil emulsion comprising an oil phase and an aqueous phase wherein the oil phase consists of fuel oil, kerosene, odorless mineral spirits or mixtures thereof, and one more surfactants at an overall HLB ranging from 8 to 11, wherein the aqueous phase is in the form of micelles and contains a crosslinked, cationic, polymer produced from 40 to 99 parts by weight of acrylamide and 1 to 60 parts by weight of a cationic monomer selected from N,N-dialkylaminoalkylacrylates and methacrylates, and their quaternary or acid salts, N,N-dialkylaminoalkylacrylamides and methacrylamides, and their quaternary or acid salts, and dialkyldimethylammonium salts. The micelles have a diameter of less than 0.1 micrometers, and the polymer has a solution viscosity of from 1.2 to 1.8 centipoise, and a content of N,N-methylenebisacrylamide of 10 molar parts to 1000 molar parts per million, based on the monomeric units present in the polymer.
U.S. Pat. No. 5,393,381 describes a process of making paper or board by adding a water-soluble branched cationic polyacrylamide and a bentonite to the fibrous suspension of pulp. The branched cationic polyacrylamide is prepared by polymerizing a mixture of acrylamide, cationic monomer, branching agent, and chain transfer agent by solution polymerization.
U.S. Pat. No. 5,431,783 describes a method for providing improved liquid-solid separation performance in liquid particulate dispersion systems. The method comprises adding to a liquid system containing a plurality of finely divided particles from 0.05 to 10 pounds per ton, based upon the dry weight of the particles, of an ionic, organic crosslinked polymeric microbead with a diameter of less than 500 nanometers, and from 0.05 to 20 pounds per ton, on the same basis, of a polymeric material selected from the group consisting of polyethylenimines, modified polyethylenimines, and mixtures thereof. In addition to the compositions described above, additives such as organic ionic polysaccharides may also be combined with the liquid system to facilitate separation of the particulate material therefrom.
U.S. Pat. No. 5,501,774 describes a process where filled paper is made by providing an aqueous feed suspension containing filler and cellulosic fiber, coagulating the fiber and filler in the suspension by adding cationic coagulating agent, making an aqueous thinstock suspension by diluting a thickstock consisting of or formed from the coagulated feed suspension, adding anionic particulate material to the thinstock or to the thickstock from which the thinstock is formed, subsequently adding polymeric retention aid to the thinstock and draining the thinstock for form a sheet and drying the sheet.
U.S. Pat. No. 5,882,525 describes a process in which a cationic branched water-soluble polymer with a solubility quotient greater than 30% is applied to a dispersion of suspended solids, e.g. a paper making stock, in order to release water. The cationic, branched, water-soluble polymer is prepared from similar ingredients to U.S. Pat. No. 5,393,381, by polymerizing a mixture of acrylamide, cationic monomer, branching agent and chain transfer agent.
U.S. Pat. No. 4,913,775 describes a process wherein paper or paperboard is made by forming an aqueous cellulosic suspension, passing the suspension through one or more shear stages selected from cleaning, mixing and pumping, draining the suspension to form a sheet, and drying the sheet. The suspension that is drained includes an organic polymeric material that is a flocculant or a retention aid, and an inorganic material comprising bentonite, which is added in an amount of at least 0.03% to the suspension after one of the shear stages. The organic polymeric retention aid or flocculant comprises a substantially linear synthetic cationic polymer having molecular weight above 500,000 and having a charge density of at least 0.2 equivalents of nitrogen per kilogram of polymer. The organic polymeric retention aid or flocculant is added to the suspension before the shear stage in an amount such that flocs are formed. The flocs are broken by the shearing to form microflocs that resist further degradation by the shearing, and that carry sufficient cationic charge to interact with the bentonite to give better retention than that which is obtainable when adding the polymer alone after the last point of high shear. This process is commercialized by Ciba Specialty Chemicals under the Hydrocol registered trademark.
U.S. Pat. No. 5,958,188 further describes a process where paper is made by a dual soluble polymer process in which a cellulosic suspension, which usually contains alum or cationic coagulant, is first flocculated with a high intrinsic viscosity (IV) cationic synthetic polymer or cationic starch and, after shearing, the suspension is reflocculated by the addition of a branched anionic water-soluble polymer having an intrinsic viscosity above 3 deciliters per gram, and a tan delta at 0.005 Hertz of at least 0.5.
U.S. Pat. No. 6,310,157 describes a dual soluble polymer process in which a cellulosic suspension which usually contains alum or cationic coagulant is first flocculated with a high IV cationic synthetic polymer or cationic starch and, after shearing, the suspension is reflocculated by the addition of a branched anionic water-soluble polymer having IV above 3 dl/g and tan delta at 0.005 Hz of at least 0.5. The process gives an improved combination of formation, retention, and drainage.
U.S. Pat. No. 6,391,156 describes a process of making paper or paper board comprising forming a cellulosic suspension, flocculating the suspension, draining the suspension on a screen to form a sheet and then drying the sheet, characterized in that the suspension is flocculated using a flocculation system comprising a clay and an anionic branched water-soluble polymer that has been formed from water-soluble ethylenically unsaturated anionic monomer or monomer blend and branching agent and wherein the polymer has an (a) intrinsic viscosity above 1.5 dl/g and/or saline Brookfield viscosity of above 2.0 mPa·s and (b) rheological oscillation value of tan delta at 0.005 Hz of above 0.7 and/or (c) deionised SLV viscosity number which is at least three times the salted SLV viscosity number of the corresponding unbranched polymer made in the absence of branching agent.
U.S. Pat. No. 6,454,902 describes a process for making paper comprising forming a cellulosic suspension, flocculating the suspension, draining the suspension on a screen to form a sheet, and then drying the sheet, wherein the cellulosic suspension is flocculated by addition of a polysaccharide or a synthetic polymer of intrinsic viscosity at least 4 deciliters per gram, and then reflocculated by a subsequent addition of a reflocculating system, wherein the reflocculation system comprises a siliceous material and a water-soluble polymer. In one embodiment, the siliceous material is added prior to or simultaneously with the water-soluble polymer. In another embodiment, the water-soluble polymer is anionic and added prior to the siliceous material.
U.S. Pat. No. 6,524,439 provides a process for making paper or paperboard comprising forming a cellulosic suspension, flocculating the suspension, draining the suspension on a screen to form a sheet and then drying the sheet. The process is characterized in that the suspension is flocculated using a flocculation system comprising a siliceous material and organic microparticles that have an unswollen particle diameter of less than 750 nanometers.
U.S. Pat. No. 6,616,806 describes a process for making paper comprising forming a cellulosic suspension, flocculating the suspension, draining the suspension on a screen to form a sheet and then drying the sheet, wherein the cellulosic suspension is flocculated by addition of a water-soluble polymer which is selected from a) a polysaccharide or b) a synthetic polymer of intrinsic viscosity at least 4 dl/g and then reflocculated by a subsequent addition of a reflocculating system, wherein the reflocculating system comprises i) a siliceous material and ii) a water-soluble polymer. In one aspect the siliceous material is added prior to or simultaneous with the water-soluble polymer. In an alternative for the water-soluble polymer is anionic and added prior to the siliceous material.
JP Publication No. 2003-246909 discloses polymer dispersions is produced by combining an amphoteric polymer having a specific cationic structural unit and an anionic structural unit and soluble in the salt solution, and a specific anionic polymer soluble in the salt solution and polymerizing them in dispersion under agitation in the salt solution.
However, there still exists a need to further enhance paper making processes by further improving drainage, retention and formation. Furthermore there also exists a need for providing a more effective flocculation system for making highly filled paper. It would be desirable if these improvements included use of polymers that require less make-down equipment, less complicated feed-systems, and environmentally friendly, e.g., polymers with low or no volatile organic chemicals (VOC).